Mariana Oyanguren, left, with City of Houston HoustonTV, hugs Houston Fire Chief Terry Garrison after a media conference in his office Friday, Nov. 15, 2013, in Houston. He spoke about his decision to resign effective at the end of the year. He spoke about the medical issues of his 20-month-old grandson, Jack Jenson, shown on his desk computer screen, as being foremost in his decision to resign. He is returning to Phoenix. less

Mariana Oyanguren, left, with City of Houston HoustonTV, hugs Houston Fire Chief Terry Garrison after a media conference in his office Friday, Nov. 15, 2013, in Houston. He spoke about his decision to resign ... more

Photo: Melissa Phillip, Houston Chronicle

Image 3 of 15

HFD Chief Terry Garrison talks with the Dowling family, including his wife, Jacki, left, as friends and family gathered in the waiting room area in support of Capt. William Dowling at Memorial Hermann Hospital Thursday, June 6, 2013, in Houston. less

HFD Chief Terry Garrison talks with the Dowling family, including his wife, Jacki, left, as friends and family gathered in the waiting room area in support of Capt. William Dowling at Memorial Hermann Hospital ... more

Photo: Johnny Hanson, Houston Chronicle

Image 4 of 15

Mary Sullivan, left, mother of firefighter Anne Sullivan, is presented a flag by Houston Fire Chief Terry Garrison during a memorial service for the fallen firefighters.

Mary Sullivan, left, mother of firefighter Anne Sullivan, is presented a flag by Houston Fire Chief Terry Garrison during a memorial service for the fallen firefighters.

Photo: Brett Coomer, Staff

Image 5 of 15

Retired Houston Fire Department retired firefighter Terry Crawford, left, and Houston Fire Department Chief Terry Garrison speak before a memorial service honoring Houston firefighters Robert Bebee, Robert Garner, Matthew Renaud, and Anne Sullivan at Reliant Stadium Wednesday, June 5, 2013, in Houston. The four firefighters died in a 5-alarm fire while searching for people they thought might be trapped inside a burning motel and restaurant last Friday. ( Brett Coomer / Houston Chronicle ) less

Houston Fire Chief Terry Garrison, left, takes a flag from a member of the HFD Honor Guard during a memorial service honoring Houston firefighters Robert Bebee, Robert Garner, Matthew Renaud, and Anne Sullivan at Reliant Stadium Wednesday, June 5, 2013, in Houston. The four firefighters died in a 5-alarm fire while searching for people they thought might be trapped inside a burning motel and restaurant last Friday. less

Houston Fire Chief Terry Garrison, left, takes a flag from a member of the HFD Honor Guard during a memorial service honoring Houston firefighters Robert Bebee, Robert Garner, Matthew Renaud, and Anne Sullivan ... more

Photo: Brett Coomer, Houston Chronicle

Image 7 of 15

Fire Chief Terry Garrison, left, and Rick Flanagan

Fire Chief Terry Garrison, left, and Rick Flanagan

Photo: Dave Rossman, Freelance

Image 8 of 15

Houston Fire Chief Terry Garrison leaves after escorting the bodies of the four fallen firefighters drive to the Forensic Center of Harris County to be examined, Friday, May 31, 2013, in Houston. The firefighters died fighting a five-alarm fire at the Southwest Inn earlier in the day. less

Houston Fire Chief Terry Garrison leaves after escorting the bodies of the four fallen firefighters drive to the Forensic Center of Harris County to be examined, Friday, May 31, 2013, in Houston. The ... more

Photo: Cody Duty, Houston Chronicle

Image 9 of 15

Houston Fire Department Chief Terry Garrison speaks during a news conference at the fire department's headquarters Friday, Jan. 27, 2012, in Houston. He spoke about the arrest of Captain Saul Fiszer who was arrested for charges in a sex case. The captain was hired in April 1994. (Cody Duty / Houston Chronicle) less

Houston Fire Department Chief Terry Garrison speaks during a news conference at the fire department's headquarters Friday, Jan. 27, 2012, in Houston. He spoke about the arrest of Captain Saul Fiszer who was ... more

Houston Fire Department Chief Terry Garrison introduces himself to Adriana Bounds, 5, before the reopening celebration for Fire Station 25. The station was built in 1979 as a 7,920 square foot facility. On November 28, 2011, the station closed for renovation but remained in operation by utilizing a modular building at the same location. Repairs took over six months to complete at a cost of $1,000,240.00. The station was reopened and the firefighters moved back in on June 13, 2012. less

Houston Fire Department Chief Terry Garrison introduces himself to Adriana Bounds, 5, before the reopening celebration for Fire Station 25. The station was built in 1979 as a 7,920 square foot facility. On ... more

Photo: Nick De La Torre, Houston Chronicle

Image 12 of 15

Houston Fire Department Chief Terry Garrison speaks during a news conference at the fire department's headquarters Friday, Jan. 27, 2012, in Houston. He spoke about the arrest of Captain Saul Fiszer who was arrested for charges in a sex case. The captain was hired in April 1994.

Houston Fire Department Chief Terry Garrison speaks during a news conference at the fire department's headquarters Friday, Jan. 27, 2012, in Houston. He spoke about the arrest of Captain Saul Fiszer who was

Houston Fire Chief Terry Garrison speaks during a news conference at Fire Station 8 Friday, Nov. 18, 2011, in Houston. Chevron presented the Houston Fire Department with $88 thousand of equipment and tools used for high-rise firefighting. less

Houston Fire Chief Terry Garrison speaks during a news conference at Fire Station 8 Friday, Nov. 18, 2011, in Houston. Chevron presented the Houston Fire Department with $88 thousand of equipment and tools used ... more

Photo: Cody Duty

Image 14 of 15

Houston firefighter Kevin Story explains to the media the mechanics of the new high-rise hose strap at Fire Station 8. According to Fire Chief Terry Garrison, the more than 400 high-rise buildings in Houston require more complicated operational approaches and specific challenges to firefighters and occupants. less

Houston firefighter Kevin Story explains to the media the mechanics of the new high-rise hose strap at Fire Station 8. According to Fire Chief Terry Garrison, the more than 400 high-rise buildings in Houston ... more

Garrison, 56, had told Mayor Annise Parker he would stay five years when he was hired in September 2010, but announced less than two weeks ago he was stepping down to return to Phoenix to help care for his ailing 20-month-old grandson, Jack.

A recent change in the boy's care, however, made it more logical for the family to relocate to Houston, with its renowned Texas Medical Center, Garrison said Tuesday.

"We initially felt Phoenix was the best place logistically to care for our grandson. However, shortly after submitting my resignation, there was a major change in his health care needs that makes Houston and the Texas Medical Center our best hope in moving Jack's health in a positive direction," Garrison wrote in a letter to fire department staff. "I look forward to continuing as Fire Chief of this great city and I am comforted knowing that my family will be embraced in the same manner."

Garrison has said his family had planned to relocate to Houston, but remained in Arizona after learning of the boy's condition; the chief made frequent weekend trips to visit.

Garrison has said Jack is afflicted by a feeding disorder, causing a "failure to thrive." He said the toddler weighs only about 19 pounds and is fed through a tube in his stomach.

"Chief Garrison has made great strides for our fire department, and while I know of his family's hardships, I welcome his decision to stay in Houston to keep that momentum going," Parker said in a statement. "His family will have access to the best resources in the medical field, and that is part of what makes our city great."

Garrison began his firefighting career in 1977 with the Phoenix Fire Department, rising to assistant chief before leaving in 2007. Garrison served as fire chief for a small community in California from 2007 to 2009 and then served a brief stint as interim chief of a small department near Phoenix before coming to Houston in fall 2010.

The Garrison family is expected to relocate to Houston over the next few months.